The present invention relates to a method of disinfecting deionized water producing apparatus and a method of producing deionized water with using the electrodejonization apparatus disinfected by disinfecting method.
A conventional system for producing purified water which is employed in fields of the pharmaceutical manufacturing industry, the semiconductor manufacturing industry and the like is shown FIGS. 2a and 2b. 
FIG. 2a is a system diagram illustrating a system for producing deionized water employed in the field of the pharmaceutical manufacturing industry, in which raw water is treated with an activated carbon (AC) column or tower 2, a safety filter 3 and a membrane degassing apparatus 4 by way of a tank 1, a pump P0 and a heat exchanger HE1, and then the water is pressured by a pump P1 and treated with a reverse osmosis membrane (RO) apparatus 5 and an electrodeionization apparatus 6. After that, the water is treated with a subsystem comprising an ultraviolet (UV) disinfecting apparatus 8 and an ultra filtration (UF) membrane apparatus 9 by way of a tank 7, a pump P2 and a heat exchanger HE2, and finally the water is transported to a use point.
FIG. 2b is a system diagram illustrating a system for producing the deionized water employed in the field of the semiconductor manufacturing industry. As shown in FIG. 2b, the raw water such as city water and well water is treated with the AC column 2, the safety filter 3 and the membrane degassing apparatus 4 by way of the tank 1, the pump P0 and the heat exchanger HE, and then pressurized by the pump P1. After that, the water is treated with the RO membrane apparatus 5 and the electrodeionization apparatus 6.
Furthermore, the water is treated with a subsystem comprising a low-pressure UV oxidizing apparatus 10, a mixed-bed ion exchange apparatus 11, the UV disinfecting apparatus 8 and the UF membrane apparatus 9, and then transported to the use point.
The deionized water producing apparatus is disinfected when the operation of the apparatus is commenced or periodically as follows.
Above equipments previous to the electrodeionization apparatus 6 are disinfected with heated water or agents. For example, when the system shown in FIG. 2a is disinfected with the heated water, the water in the tank 1 is heated to 80 to 90xc2x0 C. with the heat exchanger HE1, and then the hot water is let through the AC column 2, the safety filter 3 and the membrane degassing apparatus 4, after that, the water is pressurized with pump P1 to let the water through the RO membrane apparatus 5. The reject water of the RO membrane apparatus is drained or fed back to the tank1. The permeated water of the RO membrane apparatus is drained or circulated to the tank 1.
After that, the subsystem is disinfected with heated water or agents. For example, disinfection is made in such a manner that the water in the tank 7 is heated to 80 to 90xc2x0 C. with the heat exchanger HE2 and, then, is let through the UV disinfecting apparatus 8 and the UF membrane apparatus. The reject water and the permeated water of the UF membrane apparatus 9 are drained. Furthermore, piping from the usepoint to the tank 7 is disinfected with steam.
The electrodeionization apparatus 6 is disinfected by using a germicide such as agent like H2O2. However, the efficiency of disinfection is insufficient. In case the disinfecting with agents is periodically made, it is necessary to securely manage the prevention against retention of the agents in the equipments and the piping.
As disclosed above the conventional systems for producing deionized water shown in FIGS. 2a and 2b are disinfected insufficiently and bacteria are present in product water of the electrodeionization apparatus, so that the succeeding subsystem is polluted with the bacteria within a short time. Since the bacteria are not completely removed even with the UV disinfecting apparatus, the bacteria proliferate in the system as the time elapses. That is, an ion exchanger resin or an ion exchange membrane is disinfected insufficiently, so that the bacteria are unusually present on the order of 102 to 107 per 100 cc in the product water. The number of bacteria increases as the operational time elapses to degrade the quality of the product water.
It is an object of the present invention to solve aforementioned conventional problems and to provide a method of disinfecting deionized water producing apparatus and a method of producing deionized water which prevents bacteria proliferation in the electrodeionization and provides deionized water of high quality.
A method of the invention is for disinfecting deionized water producing apparatus which has a preceding or pretreatment apparatus including a reverse osmosis (RO) apparatus, and an electrodeionization apparatus having a diluting compartment filled with an ion exchanger. According to the method, the preceding apparatus is disinfected by flowing hot water of higher than 80xc2x0 C. therethrough, and the electrodeionization apparatus is disinfected by flowing hot water of higher than 60xc2x0 C. therethrough.
The deionized water producing apparatus may be disinfected by the method of the present invention when the apparatus is started to be operated or intermittently during operation thereof, so that the number of bacteria in the deionized water flown out of the electrodeionization apparatus is kept at a low level.
The hot water to be flown into the apparatus for disinfection thereof is preferably heated or cooled at a rate of 0.1-10xc2x0 C./min in order to prevent deterioration by heat of ion exchange resin and ion exchanging membranes in the electrodeionization apparatus.
According a method of producing deionized water of the present invention, deionized water is prepared by the deionized water producing apparatus which is disinfected according to the disinfecting method of the present invention.